Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.44   13.714%   $72.1402   $72.14   $72.15   $72.10  
  Purchase #2 $45.33   9.323%   $49.5561   $49.56   $49.55   $49.60  
  Purchase #3 $95.71   6.551%   $101.98   $101.98   $102.00   $102.00  
  Purchase #4 $198.44   13.128%   $224.4912   $224.49   $224.50   $224.50  
  Purchase #5 $66.78   4.127%   $69.536   $69.54   $69.55   $69.50  
  Purchase #6 $167.68   5.710%   $177.2545   $177.25   $177.25   $177.30  
  Purchase #7 $69.62   4.595%   $72.819   $72.82   $72.80   $72.80  
  7 purchase totals = $707.00       $767.7770   $767.78   $767.80   $767.80